Cleaning units for cleaning floors are generally known. As a rule, these units include a rotating roll, for example, with a brush attachment. The roll, in addition to moving the cleaning unit across a floor surface, also rotates so as to sweep a floor surface with the brush attachment. This type of cleaning unit is frequently operated by hand. Improvements in battery technologies make it increasingly possible to manufacture automatic cleaning units that pass over a floor surface in random movements and thus clean the floor surface.
As a rule, automatic cleaning units run in a straight line across an area of the floor surface until they encounter an obstacle. After contact with the obstacle, they change direction, which as a rule is done randomly, and the cleaning unit continues to move in a different direction.
For example, U.S. Pat. No. 4,173,809 discloses a battery-operated vacuum cleaner, the drive unit of which includes spherical shells that can rotate in any direction and that can randomly change their movement in any direction.
In addition, U.S. Pat. No. 6,571,415 B2 discloses a floor cleaning system having its own drive mechanism, in which the drive unit includes a hollow spherical shell that is attached to the frame so as to rotate freely. Disposed inside the hollow spherical shell is a weighted motor which randomly moves the hollow spherical shell. This causes the cleaning system to move in random movements across the floor, thereby cleaning the floor surface.
Because of the spherical drive elements, the drive units for the cleaning systems described above have only one or few points of contact with the floor surface, which limits the transmission of the motive energy required to move the cleaning system forward. This is a disadvantage especially in cases where the cleaning system uses a cleaning cloth or a cleaning brush that is intended to have full-surface contact with the floor surface to be cleaned and therefore requires a high driving power in order to set the cleaning system into motion.
Furthermore, in addition to the driving power required to move the cleaning system across the floor surface, it is desirable for a cleaning element that is moved across the floor surface to execute an additional movement, for example, a rotational movement, so as to enhance the cleaning effect.